1. Field of the Invention
The present invention relates to a changeover of an image output mode particularly according to kinds of image data, in a print system that a print job received from a host computer connected on a network is processed by an image processing apparatus and then output to a recording medium by an image forming apparatus.
2. Related Background Art
Recently, an image processing system such as a color image printing system that print data generated on a host computer is printed by an image forming apparatus such as a color copying machine or the like through an image processing apparatus or the like develops.
In such a color image printing system, for example, as proposed by Japanese Patent Application Laid-Open Nos. 11-127353 and 2000-259819, there is conventionally a means which extracts the feature of each pixel of an image by using an image area separation means and uses the extracted feature of each pixel in an image process to improve a quality of the image to be print output.
Hereinafter, a conventional image processing system having an image area separation means will be explained with reference to FIG. 14.
FIG. 14 is a block diagram showing the structure of the conventional image processing system which is the basic type of the image processing apparatus used in Japanese Patent Application Laid-Open No. 11-127353 and the like.
As shown in FIG. 14, an input image (represented by Y (yellow), M (magenta), C (cyan) and K (black) signals) obtained from an external apparatus 3-01 is sent to a density/brightness conversion unit 3-02. Then, in the density/brightness conversion unit 3-02, the input image represented by the Y, M, C and K signals is converted into signals representing so-called additive three primary colors of R (red), G (green) and B (blue) by a not-shown an LUT (look-up table) ROM, and the converted R, G and B signals are then input to a brightness/density conversion unit 3-03 and an image area separation unit 3-07.
First, in the brightness/density conversion unit 3-03, the input R, G and B signals are converted into Y, M, C and K signals based on a so-called subtractive color mixing principle, and the obtained Y, M, C and K signals are then input to a smoothing circuit 3-04.
On the other hand, in the image area separation unit 3-07, the input R, G and B signals for each pixel are subjected to an edge detection process by an edge detection circuit 3-08 on the basis of information obtained from peripheral pixels, and an edge signal is resultingly output. Likewise, the input R, G and B signals for each pixel are subjected to a feature extraction process such as thickness discrimination or the like by a thickness discrimination circuit 3-09, and a zone signal is resultingly output. Then, on the basis of the extracted features represented by the edge and zone signals, it is discriminated by an LUT 3-10 whether the signals represent a character/graphic area or a photographic area, and the discriminated result represented by an SEN signal is notified to the smoothing circuit 3-04.
Next, in the smoothing circuit 3-04, a smoothing process is performed only to the character/graphic area on the basis of the image area separation result (SEN signal) sent from the image area separation unit 3-07. More specifically, in the smoothing circuit 3-04, a changeover of 400 dpi/800 dpi lines is performed for each pixel in accordance with the image area separation result (represented by the SEN signal) sent from the image area separation unit 3-07, data having twice resolution for the input image is generated, and the obtained data is output to a gamma conversion table 3-05.
Then, in the gamma conversion table 3-05, density data of the respective resolutions is data-converted in accordance with gradation reproducibility of a printer unit 3-06.
The Y, M, C and K image signals processed as above and the SEN signal being the changeover signal of 400 dpi/800 dpi lines are sent to a laser driver provided in the printer unit 3-06, whereby recording based on these signals is performed according to a PWM (pulse width modulation) manner in the printer unit 3-06.
By the structure explained as above, in the conventional image processing system, a satisfactory image according to a kind of image can be obtained.
However, in the conventional image processing system, it is possible to change the process by sending an attribute signal to the smoothing circuit 3-04, according to which of character, graphic and photograph the attribute of each object indicates. However, the image area can not be completely separated by the image area separation unit 3-07. That is, in some cases, image quality rather occasionally decreases due to misjudgment concerning the image area.
However, since the print data (assumed to be PDL (page description language) data in this case) to be processed by the image processing apparatus includes the description for representing the attribute (which of character, graphic and photograph) of each object, it is possible to generate the attribute signal to each object and then send it to the above smoothing circuit, whereby the problem of misjudgment as above can be solved.
However, when the data of each pixel of each of Y, M, C and K is eight-bit data, if the attribute signal is added to the data of each pixel as above, the obtained data is necessarily processed as nine-bit data, whereby various new problems occur. More specifically, more memories are needed because a data amount increases by one bit for each data, and an increase of image data capacity influences a transfer speed of the image data.